As an angle adjuster for adjusting the inclination angle of a back frame of a reclining chair as one example of furniture, various structures are known, as disclosed in, e.g., Japanese Unexamined Patent Application Publication No. 2002-177082 (Patent Document 1), Japanese Unexamined Patent Application Publication No. 2006-230720 (Patent Document 2) and Japanese Unexamined Patent Application Publication No. 2006-340798 (Patent Document 3).
Such an angle adjuster is equipped with a first arm and a second arm. The first arm and the second arm are connected so that the second arm is rotatable relative to the first arm. Also, a seat frame is attached to the first arm and the back frame is attached to the second arm. Such an angle adjuster is structured so as to be able to adjust a development angle of the second arm to the first arm in a stepwise manner using engagement of gear teeth and a ratchet claw. Therefore, the development angle of the second arm cannot be adjusted steplessly, so fine angle adjustments corresponding to a user's liking and degree of fatigue could not be performed. Also, when rotating the second arm in a forward rotation direction to adjust the development angle of the second arm (e.g., a direction to reduce the development angle of the second arm), there is a drawback that a “click” sound is produced to bother people around the user.
The angle adjuster disclosed in Japanese Unexamined Patent Application Publication No. 2009-45395 (Patent Document 4) is capable of adjusting the development angle of the second arm to the first arm in a non-stepwise manner.
In this angle adjuster, a cylindrical fixed boss portion is provided at the first arm (immovable metal fitting) in a fixed and protruded manner, and a rotation boss portion is integrally provided at a second arm (movable metal fitting) so as to rotate together with the second arm. The base portion of the rotation boss portion is inserted into the fixed boss portion from the tip end side of the fixed boss portion in a rotatable manner, and the tip portion of the rotation boss portion is arranged so as to protrude from the tip end of the fixed boss portion. A twist coil spring is outwardly fitted on the fixed boss portion. One end portion of the twist coil spring is fixed to the tip end of the rotation boss portion and the other end portion of the twist coil spring is fixed to the first arm. When the rotation boss portion of the second arm rotates in a reverse rotation direction, the one end portion of the twist coil spring rotates integrally with the rotation boss portion, reducing the diameter of the twist coil spring to thereby wind and tighten the outer peripheral surface of the fixed boss portion, which in turn prevents the rotation of the second arm in the reverse rotation direction.